1. Field of the Invention
The present invention relates to an RF switch and, more particularly, to an RF switch in which power of an amplifier is adjusted by a Schmitt trigger circuit.
2. Description of the Background Art
In general, an RF switch is a device for changing a path of an RF signal by an input signal of a user, and various models are used depending on its use.
FIG. 1 illustrates a general RF switch.
As shown in FIG. 1, the RF switch receives an air radio frequency (RF) signal or a cable radio frequency (RF) signal from an external source and transmits it to a tuner or a ¾ modulator.
That is, the RF switch includes two output terminals, and when the same signal is outputted through the two output terminals, one is inputted to the tuner and the other is inputted to the ¾ modulator in a standby state for a loop-out.
FIG. 2 is a block diagram showing an internal construction of the conventional RF switch.
As shown in FIG. 2, the conventional RF switch has such a structure that an RF signal is received from an external source, the RF signal of a terminal selected by a relay switch is amplified, and two same signals are outputted through a splitter.
The conventional RF switch will now be described in detail.
First, a power supply and relay switch adjusting interface 204 performs an interface control between a user and the relay switch, and supplies power to each part of the RF switch.
The relay switch 201 receives the RF signal, selects a received air RF signal or cable RF signal under the control of a relay switch adjusting unit 205 according to a user's selection, and outputs it to an amplifier 202.
Then, the amplifier 202 amplifies the air RF signal or cable RF signal outputted through the relay switch 201 to a predetermined level, and outputs it to the splitter 202.
The splitter 203 outputs the amplified RF signal simultaneously to the tuner and the ¾ modulator through a first output port and a second output port. At this time, the amplifier 202 not only compensates a signal attenuation phenomenon due to the relay switch 201 or the splitter 203 but also maintains a signal flatness according to a frequency in a broadband to its maximum. Thus, in measuring an infinitesimal signal receiving performance, a better performance is shown at a higher frequency.
However, in measuring a strong signal performance, the performance is degraded due to the amplifier 202, and in an area where an analog signal and a DTV signal having high signal strengths over broadband are received adjacently, or in a vicinity of a transmitting station, a distortion is generated in the amplifier 202, so that an image is broken or a specific channel is not taken. This is called an overload phenomenon of the amplifier 202. This phenomenon actually takes place in the North America, and in order to avoid such a phenomenon and the performance degradation in inputting a strong signal, several methods are used.
FIG. 3 is a block diagram showing an internal construction of the conventional RF switch for preventing a performance degradation in inputting a strong signal.
As shown in FIG. 3, the conventional RF switch for preventing a performance degradation has a structure that switches 302 and 304 are connected to input/output terminal of an amplifier 303 and a microcomputer 309 controls switching of the switches 302 and 304 through an input port 308, in addition to the structure of FIG. 2.
That is, the output of the relay switch 301 is outputted to the switch 302, and the switch 302 is switched under the control of the microcomputer 309 to output an inputted signal to the amplifier 303 or to the switch 304. Likewise, the switch 304 is switched under the control of the microcomputer 309 and selects a signal outputted from the amplifier 303 to output it to the splitter 305 or selects a signal outputted from the switch 302 to output it to the splitter 305.
In other words, according to the switching of the switches 302 and 304, the output of the relay switch 302 can be outputted to the splitter 305 through the amplifier 303 or directly bypassed to the splitter 305 without passing through the amplifier 303. Therefore, with the strong signal or the overload, the conventional RF switch as shown in FIG. 3 has a better performance than the conventional RF switch as shown in FIG. 2.
However, the switches 302 and 304 keeps operating in the vicinity of a threshold value adjusting a signal path which does not pass through the amplifier 303 and a signal path which passes through the amplifier 303. This causes a malfunction in the tuner, so that an image is broken even at a general signal or a non-image phenomenon occurs. Due to this phenomenon, the RF switch as shown in FIG. 3 is not used presently any longer.
In a different method for preventing the performance degradation caused by the RF switch as shown in FIG. 2, the amplifier is removed form the RF switch. This method shows a good performance over the strong or the overload, but since a signal attenuation according to the splitter is not compensated, an infinitesimal signal performance is not good.
In a still different method for preventing the performance degradation caused by the RF switch as shown in FIG. 2, an RF switch having an amplifier is used and in an area where a strong signal is generated, a user is recommended to install an attenuator at an input terminal of the RF switch. This method, however, has a problem that since there is a wide deflection in the signal strength depending on a channel or a direction of an antenna, it is not easy for the user to determine and control the signal performance.